Up till now, in mobile communication, ARQ (Automatic Repeat reQuest) is applied to uplink data from a radio communication mobile station apparatus (hereinafter abbreviated to “mobile station”) to a radio communication base station apparatuses (hereinafter abbreviated to “base station”), and a response signal representing error detection results of uplink data is fed back to the mobile station in downlink. A CRC (Cyclic Redundancy Check) is performed for uplink data, and an ACK (ACKnowledgement) is fed back if CRC=OK (no error), or a NACK (Negative ACKnowledgement) is fed back if CRC=NG (error present), as a response signal to the mobile station.
Recently, to use downlink communication resources efficiently, studies are underway for ARQ in which channels for response signals are shared for use between a plurality of mobile stations. Further, in this ARQ, a base station feeds back a response signal to a mobile station a predetermined time after receiving uplink data. If a NACK is fed back from the base station, the mobile station retransmits uplink data to the base station a predetermined time after receiving the NACK signal. Further, in this ARQ, information indicating to which mobile station a response signal is directed, is not attached to the response signal (see Non-Patent Document 1).
Also, a base station transmits allocation information indicating to which mobile station among a plurality of mobile stations an uplink data channel is allocated, on a per mobile station basis. Allocation information of each mobile station includes mobile station ID information indicating to which mobile station the allocation information is directed. For example, allocation information includes, as mobile station ID information, CRC bits masked by the ID number of the destination mobile station of that allocation information. Each mobile station decides that allocation information of CRC=OK (no error) acquired by demasking allocation information by the ID number of that mobile station, is allocation information directed to the subject mobile station. Thus, a mobile station performs blind detection as to whether or not allocation information is directed to that mobile station.    Non-Patent Document 1: 3GPP RAN WG1 meeting document, R1-070245, “Modifications of Uplink Synchronous HARQ scheme”, LG Electronics